During the processing or storage of waste, for instance, residential or industrial waste, the waste may be concentrated into piles, for example, within landfills, compost windrows, and sludge heaps, among others. When waste is concentrated into piles, it is often necessary to cover the waste piles to minimize the emission of odor, prevent fires, prevent the movement of the waste, and/or prevent vectors such as birds, flies, and other insects from feeding on the waste. Typically, waste piles are covered by spreading a layer of dirt over the exposed portions of the waste piles. For example, in landfills, piles of municipal solid waste are typically covered by spreading a layer of dirt on the pile. The thickness of the layer depends upon the length of time the pile is to remain covered. For example, a waste pile that is to be covered for a short period of time, for example, overnight, may require, for example, a six-inch layer. However, when it is necessary to cover a waste pile for a relatively longer period of time, a twelve-inch layer may be required. For a permanent cover generally a layer of dirt of approximately two feet or more in thickness may be required.
One problem associated with the use of soil and dirt is that large quantities are necessary to cover these waste piles. For this reason, there is a high loss of available volume for waste thereby significantly reducing the amount of waste that can be concentrated into a pile. This is particularly true in landfills where waste piles are stacked upon other waste piles having daily soil covers separating each waste pile. Since there is concern over the effective space available in existing landfills, it has become necessary to maximize the volume available for waste. One way of accomplishing this is to minimize the volume of dirt necessary for covering the waste piles or to provide a cover material that substitutes for the dirt.
Several spray-on coatings have been developed to provide an effective cover to waste piles. These include the coatings described in U.S. Pat. Nos. 5,161,915; 5,275,508; 5,385,429; and 5,525,009 (the disclosures of which are incorporated by reference here in their entirety), which are marketed under the registered trademark POSI-SHELL by Landfill Service Corporation of Apalachin, N.Y. These cover materials typically comprise a mixture of water, mineral binder (such as cement kiln dust, “CKD,” or similar materials), and fibers (both cellulose and synthetic) that can be sprayed on to a waste pile and allowed to set to provide an effective cover. These mineral-based covers have proven to provide effective covers to landfills and other waste piles.
However, though cover compositions having mineral binders such as described in the above patents have been proven to provide good cover adhesion and sufficient solids content to provide good opacity, the availably of mineral binders, such as CKD, has been markedly reduced. Changes in the process of manufacturing cement and the adoption of these mineral binders for other higher value applications have reduced the supply of such mineral binders or increased there cost whereby such binders are unavailable or cost prohibitive. In attempts to replace this supply of mineral binders some have used more expensive Portland cement or other mineral binders, such as coal fly ash. However, in addition to the expense, such substitute mineral binders typically can be difficult to obtain and the quality of the substitute that is available typically exhibits inconsistent properties. One aspect of the present invention provides a cover material that employs mineral binders that is more readily available and more cost effective, while providing the desired consistency, adhesion, opacity, and durability in the material cover.
Other prior art cover materials, for example, those described in U.S. Pat. Nos. 5,082,500 and 5,516,830, are primarily fiber based. These fiber based cover materials also include clay and a polymer that aid in retaining the integrity of the fiber-based matrix. These prior art covers are predominantly fiber with minor amounts of clay binder. However, these fiber-based covers typically do not adhere well to low friction surfaces, for example, plastic containers, typically found in landfills, and thus their effectiveness as covering material can be significantly hampered. Since the fiber in the fiber-based covers tends to agglomerate or flocculate, it is inherently difficult to fluidize the fiber based slurry in order to pump and spay these fiber-containing products effectively. Accordingly, these fiber-based cover materials typically require inordinately large water content to prevent agglomeration of the fibers. However, the high water content produces a slurry that does not adhere well to refuse, most notably to plastic surfaces that are common in landfills. The tendency of such fiber-based cover materials to slide off landfill material typically requires that the material be applied repeatedly and with constant vigilance during application to areas where the cover thins or gaps appear. As a result, the application of such fiber-based covers can be problematic to ensure the desired material cover.
Moreover, the low solids content of such fiber-based cover materials provides a non-uniform cover that, when subjected to rain and wind, can lose its integrity. Typically, these limitations of the fiber-based covers may be overcome with the addition of expensive additives, such as cellulose polymers, to the mixture.
Aspects of the present invention overcome these and other limitations of the prior art and provide an effective bulk material pile cover that can be easily applied and maintained without the limitations and disadvantages of prior art material cover materials. Aspects of the present invention provide improved adhesion to landfill materials that are easier to apply with minimal concern for thinning and can be spray applied quickly and easily. Aspects of the invention also allow for easier and quicker equipment clean up.